Round balers generally have a bale forming chamber defined by a pair of opposing side walls associated with an array of side-by-side belts, transverse slats trained on chains, a plurality of transverse rollers or a combination of these various elements, e.g. rollers and belts. During field operation, windrowed crop material such as hay is picked up from the ground and fed in a continuous stream into a fixed or variable diameter chamber. The hay is rolled into a cylindrical package within the chamber, wrapped with twine, netting or a plastics film and ejected onto the ground for subsequent handling.
U.S. Pat. Nos. 5,289,672 and 4,956,968 disclose one type of prior art round baler of the general nature described above. In this particular type of baler an expandable chamber is defined by a pair of fixed sidewalls, and a plurality of side-by-side belts cooperating with a series of transverse rollers, mounted between a pair of pivotally mounted arms. This arrangement of rollers and arms is commonly referred to as a sledge assembly. The chamber includes an inlet opening in the front through which crop material is fed. Also included is a pair of take-up arms pivotally mounted on the main frame, between which arms a pair of guide rollers are journalled. A biasing force on the take-up arms urges the outer surfaces of the guide rollers against the belts to maintain tension and thereby prevent slack from occurring in the belts during expansion and contraction of the chamber. Density of the bale can be affected by varying the force on the take-up arms.
Another type of prior art round baler of the same general nature employs a plurality of transverse rollers to define a cylindrical bale forming chamber with a fixed diameter. Examples of this type of baler are shown in, U.S. Pat. Nos. 4,604,848 and 4,841,851. It should be noted that the latter patent shows additional embodiments wherein a fixed chamber is defined by means other than rollers, i.e. belts (FIG. 7) or chains and slats (FIG. 8).
The present invention relates to a wrapping system for a round baler in which a cylindrical package of crop material is formed in a fixed or expanding chamber which includes one or more transverse rollers or a combination of belts and rollers of the general nature described in U.S. Pat. No. 5,289,672, cited above. This is one example of the many prior art patents that disclose this type of expandable chamber round baler.
It is not uncommon in prior art round balers having this general configuration to feed the wrapping material between a pair of transverse rollers. Alternatively, the chamber could comprise fixed side walls and transverse elements at fixed locations in a configuration of the general nature described in U.S. Pat. No. 4,612,855, cited above.
There is a need for a wrapping system for round balers that consistently introduces wrapping material to the periphery of the cylindrical package formed in the chamber regardless of whether the diameter of the chamber is fixed or variable, and regardless of the nature of the transverse wall, i.e. belts, rollers or chains. More particularly, there is a need for a system that consistently initiates the wrapping function. Such system contributes to improved performance and operability of round balers. Additionally, the features thereof should be consistent with lower manufacturing costs without detracting from simplicity of field operation and serviceability.
EP 0 965 263 discloses a round baler having means for feeding wrapping material from a supply roll of wrapping material into the chamber between two transverse rollers for wrapping around the outer surface of the cylindrical package of crop material to form a round bale of crop material. The two transverse rollers may either be in direct contact with the crop or they may be the drive or guide rollers of a belt or apron which engages the crop. The teaching in EP 0 965 263 is to provide feed assist means extending from the transverse rollers for intermittent contact with the wrapping material as it is being dispensed into the chamber under conditions where the outer surface of a cylindrical package of crop material is being wrapped in the chamber.
An alternative design of the assist means for feeding wrapping material from a supply roll can be seen on a BR7 40 Round Baler from New Holland and is also described in U.S. Pat. No. 6,550,218. The assist means are coupled to a knife linkage which will rotate the knife to a home position when cutting the wrapping material.
The present invention is concerned with the means for introducing the wrapping material from a supply roll into the chamber. These means are constituted in EP 0 965 263 and U.S. Pat. No. 6,550,218 by a device also known, and referred to herein, as a duck bill. A duck bill is formed by two plates of which one is spring biased towards the other. One plate is fixed between two end plates, also called the duckbill cams, and the other is hinged and spring biased towards the fixed plate, the wrapping material being gripped between the free edge of the spring biased plate and the fixed plate. Such a design acts as a one-way clutch which allows the wrapping material to move in only one direction through the duck bill.
The end plates are arranged to move both plates of the duck bill between a retracted position and an advanced position. When the duck bill is moved into its advanced position, its two plates pass between two transverse rollers and pull the leading edge of the wrapping material into the bale forming chamber. Once the wrapping material is engaged by the rotating crop or one of the two transverse rollers, normally the lower roller, it is carried around the bale that is being formed and the required wrapping material is drawn freely from the supply roll through the duck bill. While the bale is being wrapped or after wrapping has ended, the duck bill is withdrawn to its retracted position. Towards the end of the baling cycle, a cutter is used to sever the wrapping material at a point between the duck bill and the wrapped bale. The material to one side of the cutter is drawn into the bale forming chamber by the rotating bale while the free end of the wrapping material from the supply remains gripped between the two plates of the duck bill in readiness to wrap the bale that is formed in the next baling cycle.
A problem is encountered with this form of duck bill, which is especially pronounced when the wrapping material is a plastics sheet coated on one side with an adhesive. Between wrapping cycles, the supply roll is locked to prevent further wrapping material from being drawn from it. However, despite the feed clutch action of the duck bill, it is found that the short length of wrapping material that remains protruding from the duck bill immediately after operation of the cutting device, tends to creep back between the plates of the duck bill towards the supply roll. This creeping of the wrapping material may be the result of a variety of causes, amongst them wind, vibration, and the action of a spreader roller incorporated in the duck bill which prevents the wrapping material from bunching in the middle and spreads it over the full width of the buck bill and the bale.
If the wrapping material creeps back to such an extent that its free end is drawn back through the duck bill, then this will prevent the wrapping material from being taken up by the newly formed bale in the following wrapping cycle. Even if not fully drawn back through the duck bill, the slack in the wrapping material between the duck bill and the supply roll can result in the material being wrapped around the spreader roller. Because the wrapping material is designed to adhere to itself, clearing the resulting feed jam and rethreading the wrapping material through the duck bill is a difficult and time consuming task.